kernel/sync/lock/
spinlock.rs

1// SPDX-License-Identifier: GPL-2.0
2
3//! A kernel spinlock.
4//!
5//! This module allows Rust code to use the kernel's `spinlock_t`.
6
7/// Creates a [`SpinLock`] initialiser with the given name and a newly-created lock class.
8///
9/// It uses the name if one is given, otherwise it generates one based on the file name and line
10/// number.
11#[macro_export]
12macro_rules! new_spinlock {
13    ($inner:expr $(, $name:literal)? $(,)?) => {
14        $crate::sync::SpinLock::new(
15            $inner, $crate::optional_name!($($name)?), $crate::static_lock_class!())
16    };
17}
18pub use new_spinlock;
19
20/// A spinlock.
21///
22/// Exposes the kernel's [`spinlock_t`]. When multiple CPUs attempt to lock the same spinlock, only
23/// one at a time is allowed to progress, the others will block (spinning) until the spinlock is
24/// unlocked, at which point another CPU will be allowed to make progress.
25///
26/// Instances of [`SpinLock`] need a lock class and to be pinned. The recommended way to create such
27/// instances is with the [`pin_init`](pin_init::pin_init) and [`new_spinlock`] macros.
28///
29/// # Examples
30///
31/// The following example shows how to declare, allocate and initialise a struct (`Example`) that
32/// contains an inner struct (`Inner`) that is protected by a spinlock.
33///
34/// ```
35/// use kernel::sync::{new_spinlock, SpinLock};
36///
37/// struct Inner {
38///     a: u32,
39///     b: u32,
40/// }
41///
42/// #[pin_data]
43/// struct Example {
44///     c: u32,
45///     #[pin]
46///     d: SpinLock<Inner>,
47/// }
48///
49/// impl Example {
50///     fn new() -> impl PinInit<Self> {
51///         pin_init!(Self {
52///             c: 10,
53///             d <- new_spinlock!(Inner { a: 20, b: 30 }),
54///         })
55///     }
56/// }
57///
58/// // Allocate a boxed `Example`.
59/// let e = KBox::pin_init(Example::new(), GFP_KERNEL)?;
60/// assert_eq!(e.c, 10);
61/// assert_eq!(e.d.lock().a, 20);
62/// assert_eq!(e.d.lock().b, 30);
63/// # Ok::<(), Error>(())
64/// ```
65///
66/// The following example shows how to use interior mutability to modify the contents of a struct
67/// protected by a spinlock despite only having a shared reference:
68///
69/// ```
70/// use kernel::sync::SpinLock;
71///
72/// struct Example {
73///     a: u32,
74///     b: u32,
75/// }
76///
77/// fn example(m: &SpinLock<Example>) {
78///     let mut guard = m.lock();
79///     guard.a += 10;
80///     guard.b += 20;
81/// }
82/// ```
83///
84/// [`spinlock_t`]: srctree/include/linux/spinlock.h
85pub type SpinLock<T> = super::Lock<T, SpinLockBackend>;
86
87/// A kernel `spinlock_t` lock backend.
88pub struct SpinLockBackend;
89
90/// A [`Guard`] acquired from locking a [`SpinLock`].
91///
92/// This is simply a type alias for a [`Guard`] returned from locking a [`SpinLock`]. It will unlock
93/// the [`SpinLock`] upon being dropped.
94///
95/// [`Guard`]: super::Guard
96pub type SpinLockGuard<'a, T> = super::Guard<'a, T, SpinLockBackend>;
97
98// SAFETY: The underlying kernel `spinlock_t` object ensures mutual exclusion. `relock` uses the
99// default implementation that always calls the same locking method.
100unsafe impl super::Backend for SpinLockBackend {
101    type State = bindings::spinlock_t;
102    type GuardState = ();
103
104    unsafe fn init(
105        ptr: *mut Self::State,
106        name: *const crate::ffi::c_char,
107        key: *mut bindings::lock_class_key,
108    ) {
109        // SAFETY: The safety requirements ensure that `ptr` is valid for writes, and `name` and
110        // `key` are valid for read indefinitely.
111        unsafe { bindings::__spin_lock_init(ptr, name, key) }
112    }
113
114    unsafe fn lock(ptr: *mut Self::State) -> Self::GuardState {
115        // SAFETY: The safety requirements of this function ensure that `ptr` points to valid
116        // memory, and that it has been initialised before.
117        unsafe { bindings::spin_lock(ptr) }
118    }
119
120    unsafe fn unlock(ptr: *mut Self::State, _guard_state: &Self::GuardState) {
121        // SAFETY: The safety requirements of this function ensure that `ptr` is valid and that the
122        // caller is the owner of the spinlock.
123        unsafe { bindings::spin_unlock(ptr) }
124    }
125
126    unsafe fn try_lock(ptr: *mut Self::State) -> Option<Self::GuardState> {
127        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
128        let result = unsafe { bindings::spin_trylock(ptr) };
129
130        if result != 0 {
131            Some(())
132        } else {
133            None
134        }
135    }
136
137    unsafe fn assert_is_held(ptr: *mut Self::State) {
138        // SAFETY: The `ptr` pointer is guaranteed to be valid and initialized before use.
139        unsafe { bindings::spin_assert_is_held(ptr) }
140    }
141}
kernel/sync/lock/spinlock.rs

kernel/sync/lock/
spinlock.rs
